1. Field of the Invention
The present invention relates to a manufacturing method of a display device and it particularly relates to a technique effective to application for a manufacturing method of forming a driving circuit having semiconductor devices on the outside of a display region including an assembly of pixels having TFT devices.
2. Description of the Related Art
Existent liquid crystal display devices having liquid display panels in which a liquid crystal material is sealed between a pair of substrates include active matrix type TFT liquid crystal display devices. The active matrix type TFT liquid crystal display device is used generally, for example, as displays of television receivers or personal computers (PC) and display areas for mobile telephone terminals or personal digital assistances (PDA).
In a liquid crystal display panel used for the active matrix type TFT liquid crystal display device, a plurality of scanning signals lines, a plurality of video signals lines, TFT devices, pixel electrodes, and the like are disposed on one of substrates.
Generally, in an existent liquid crystal display device, a flexible circuit substrate such as TCP or COF mounted with a driver IC for inputting video signals (sometimes also referred to as gradation data) to the plurality of video signal lines or a driver IC for inputting scanning signals to the plurality of scanning signal lines is connected to the liquid crystal display panel, or each of the driver IC is mounted directly on the liquid crystal display panel.
Further, in recent years, a liquid crystal display panel in which a driving circuit having a function equivalent with that of the driver IC (peripheral circuit) is formed to the outside of the display region of a substrate formed with the scanning signal lines (hereinafter referred to as a TFT substrate) is proposed for instance.
The driving circuit formed to the outside of the display region of the TFT substrate is mainly constituted with semiconductor devices such as transistors or diodes and the electrodes for each of the semiconductor devices are formed upon forming the scanning signal lines or the video signal lines, and the semiconductor layer of the semiconductor device is formed upon forming the semiconductor layer of the TFT device (channel layer) of the display region. For the semiconductor layer of the TFT device formed in the display region of the TFT substrate, an amorphous silicon (a-Si) or a polycrystal silicon (poly-Si) is used for instance.
By the way, polycrystal silicon is used preferably for the semiconductor layer of the semiconductor device in the driving circuit in view of the operation characteristics. In this case, a method of polycrystallizing the entire surface of an amorphous silicon on a substrate by dehydrogenating amorphous silicon by a heat treatment, and irradiating and scanning a pulse laser such as an excimer laser to the dehydrogenated amorphous silicon while displacing the same stepwise little by little so as to be irradiated by plural times for one position.
Further, JP-A-2002-158173 and JP-A-2002-64060, for example, disclose a method of hydrogenating an amorphous silicon by using a laser beam instead of heat treatment. In JP-A-2002-158173, dehydrogenation is conducted by a first excimer laser and polycrystallization is conducted by a second excimer laser. Further, in JP-A-2002-64060, a pulse laser beam is bisected and dehydrogenation is conducted by a preceding beam and polycrystallization is conducted by a beam succeeding thereto.
Further, although not intended for dehydrogenation, JP-A-Hei-6-61172 discloses of conducting annealing by two lasers of different energy density in relation with the use of the two lasers. A pulse layer or a continuous oscillation laser is used for the two lasers.
Further, JP-A-Hei-8-129189 discloses a method of polycrystallization only in the driving circuit portion instead of polycrystallization over the entire surface of an amorphous silicon. In JP-A-Hei-8-129189, upon constituting the pixel with hydrogenated silicon and the driving circuit with polycrystal silicon, one pulse laser is used, the energy of the pulse of the laser light is increased stepwise and crystallization is conducted while dehydrogenating the hydrogenated amorphous semiconductor only in the driving circuit portion.
In a case of manufacturing a TFT substrate using an amorphous silicon for the semiconductor layer of a TFT device in a display region and using a polycrystal silicon for the semiconductor layer of a semiconductor device in a driving circuit to the outside of the display region, while it is preferred to use a hydrogenated amorphous silicon as the amorphous silicon in view of the characteristics, since bumping occurs upon irradiation of a laser unless dehydrogenation is conducted upon polycrystallization, it is necessary for partial dehydrogenation only for the driving circuit portion.
However, since the partially dehydrogenated region and the crystallized region completely coincide to each other in JP-A Nos. 2002-158173 and 2002-64060, and 8-129189, in a case where the position for irradiation is displaced upon irradiation of a laser for conducting crystallization, the laser for crystallization may possibly be irradiated to the not dehydrogenated region at the boundary between the hydrogenated region and the not dehydrogenated region and, as a result, bumping may possibly occur.
While dehydrogenation is not described in JP-A No. Hei 6-61172, since the two laser irradiation regions coincide to each other, it is considered that a similar problem may occur in a case of intending application to the hydrogenation and the crystallization.
Further, the pulse laser is a laser intermittently emitting (generating) a light at a time interval. Accordingly, in a case of melting and crystallizing an amorphous silicon into polycrystals by irradiation of the pulse laser, this results in a problem that the size of individual granular crystals is small to form a number of crystal grain boundaries. As a result, it results in a problem that the carrier mobility is low in the TFT device of the driving circuit, failing to obtain sufficient transistor characteristics.
The present invention intends to provide a technique capable of improving the quality of a polycrystal silicon upon dehydrogenating and polycrystallizing an amorphous silicon at the outside of a display region of a substrate.
The invention further intends to provide a technique capable of improving the manufacturing efficiency of a TFT substrate using an amorphous silicon for a semiconductor layer of a TFT device in a display region and using a polycrystal silicon for the semiconductor layer of the semiconductor device of the driving circuit at the outside of the display region.
The foregoing and other objects and novel features of the present invention will become apparent in view of the descriptions of the present specification and the accompanying drawings.